Committing to SVN securely from a web application

Verbatim is the second project I've been the lead on recently where the requirements included people committing to SVN as themselves via the application. At first glance this means storing the authentication tokens of the user in plain text since we'll need to pass them along to SVN whenever they commit. I wasn't happy with that solution so after a bit of thinking we came up with an idea that leaves everything encrypted and doesn't cache any credentials. It involved minimal code in Verbatim and minor work on the SVN server.

On the SVN server the first thing we did was to create a special Verbatim user that can commit to SVN via SSH using a generated key. We copied this key to the Verbatim host which allowed us to commit as the verbatim user without typing a username or password.

The only thing that was added to the Verbatim code was a patch that Dan Schafer cooked up that sets an SVN revision property, translate:author, to the name of the current user. When the user clicks "commit" this property is set and sent along with the commit.

At this point we could commit from the application but it still goes to the application as the Verbatim user. We used SVN's hooks to take the next step.

The first script we changed was the pre-revprop-change hook. This controls what special revision properties a user can modify when they commit. Our script adds the ability to modify svn:author and translate:author. Before allowing the modifications the script checks if the user committing is the special verbatim user to prevent anyone from committing as someone else.

Next we added a post-commit script that looks for the translate:author property. If it's found it will take that value, replace svn:author, and remove translate:author; effectively making whatever was in translate:author the real author. This is a non-versioned change which means there is no commit that needs to happen - the new author is set immediately.

With these scripts in place we can commit as anyone from the application and everyone's credentials stay encrypted and secure.

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